1. Technical Field
The present invention relates to a bidirectional device, a bidirectional device circuit, and a power conversion apparatus.
2. Related Art
A conventional power conversion apparatus is known, such as a matrix converter that performs a power conversion on AC power input thereto, and outputs the resulting power. This power conversion apparatus uses a bidirectional switch capable of causing current to flow in two directions. It is known that a power device, such as a reverse-blocking IGBT that has a breakdown voltage in the reverse direction, can be used as the bidirectional switch (for example, see Non-Patent Documents 1 and 2 and Patent Document 1). Furthermore, a thyristor with an insulating gate is known that forms a bidirectional switch by forming a transistor on both surface sides of the substrate (for example, see Patent Document 2).    Non-Patent Document 1: H. Takahashi, et al., “1200V class Reverse Blocking IGBT (RB-IGBT) for AC Matrix Converter”, Proceedings of 2004 International Symposium on Power Semiconductor Devices & ICs, Kitakyushu, p. 121    Non-Patent Document 2: T. Naito, et al., “1200V Reverse Blocking IGBT with low loss for Matrix Converter”, Proceedings of 2004 International Symposium on Power Semiconductor Devices & ICs, Kitakyushu, p. 125    Patent Document 1: Japanese Patent Application Publication No. 2002-319676    Patent Document 2: Japanese Patent Application Publication No. H3-194971
The bidirectional switch can be formed by connecting two transistors in parallel. However, when forming a bidirectional switch with a normal IGBT, the IGBT has low breakdown voltage in the reverse direction, and therefore each IGBT must be provided with a diode to guarantee the breakdown voltage in the reverse direction. In contrast, with a reverse-stopping IGBT, the transistor itself has a high breakdown voltage in the reverse direction, and therefore the bidirectional switch can be formed by two transistors.
However, even when using a reverse-stopping IGBT, it is necessary to use two transistors in order to form the bidirectional switch. Therefore, the size of the module is increased. It is possible to reduce the module size by forming the transistors on both surfaces of the substrate, but forming elements on both sides of the substrates makes mounting difficult, and so this is not a practical solution. Furthermore, in recent years, in order to provide a power device with little loss, semiconductors with a large bandgap such as SiC or GaN are being used as the semiconductors in power devices. However, a MOSFET and a JFET are usually used in a longitudinal power device. Since there is no inherent reverse breakdown voltage in such devices, a reverse-stopping power device cannot be formed, and the only means available has been to combine diodes to use as the bidirectional switch.